MOCVD is a widely used process for depositing semiconductors and other materials in a growth chamber. It is very useful to monitor the growth of material in the growth chamber, and X-ray diffraction is a promising tool for this. There is also a need for monitoring growth in other types of growth chamber.
However, the construction of growth chambers leads to problems for X-ray diffractometers in that their construction necessarily needs to be optimised for growth and not for X-ray diffractometry.
Conventional X-ray diffraction approaches use a goniometer to orient incident and diffracted X-ray beams, but goniometers are difficult to use during growth and generally require a specially designed growth chamber.
Niggemeier et al, “X-Ray Reflectometer for the Diagnostics of Thin Films During Growth”, J. App. Cryst. (1997), Vol. 30, pages 905 to 908, described a reflectometer for use with a sample stage in a growth chamber in which a line X-ray source is used to illuminate a curved-crystal monochromator, known as a curved-crystal monochromator, which directs X-rays through a window in the growth chamber onto a sample stage at a glancing angle. The X-rays are diffracted by the crystal and the X-rays diffracted at a glancing angle pass out to an X-ray detector through another window.
A similar, though somewhat later approach, is described in U.S. 2001/0043668 to Hayashi et al.
However, when a sample is mounted in a growth chamber, it is normally mounted on a rotating stage which will inevitably wobble somewhat, especially since excessive time taken to align the sample and axis of rotation would be prohibitive in a production environment. There is accordingly a need for a system that can cope with this wobble and accordingly take measurements during growth.
There is a further need for a system that can work quickly to enable results to be immediately available to allow the growth to be controlled on the basis of the measurements made.